Method of producing lead coated copper sheets



G. LEBRUN 3,329,589

METHOD OF PRODUCING LEAD COATED COPPER SHEETS July 4, 1967 Filed March 5, 1965 Fig.3

United States Patent 3,329,589 METHOD OF PRODUHNG LEAD COATED COPPER SHEETS Gaston Lebrnn, Meurchin, France, assignor t0 Houilleres du Bassin du Nord et du Pas-de-Calais, Douai (Nerd), France, a French public establishment, organized under the laws of France Filed Mar. 5, 1963, Ser. No. 263,029 Claims priority, applicatitrifirance, Mar. 7, 1962, 5 2 Claims. (Cl. 204-12) This invention relates to a method of producing composite copper-lead laminate material by an electrodeposition process.

Lead-coated copper sheet has many important uses in engineering, wherever it is desired to protect a copper surface from corrosion by atmospheric and other deleterious agents. Such uses include weatherproof roofing material in building construction to prevent attack of the copper by the sulfuric acid produced by oxidation and dissolution of the sulfur content in flue gases by atmospheric oxygen and humidity; corrosion-resisting lining material in tanks and other vessels in various chemical plants; lead-lined tubing for heat-exchangers and the like.

Heretofore the lead plating of copper sheet has usually been effected by dripping the copper sheet in a bath of molten lead, sometimes also by spraying methods. In view of the lack of chemical aflinity and the low mutual solubility between copper and lead, it has been generally considered necessary, in order to ensure a satisfactory bond between the copper and lead constituents, to include a third ingredient having affinity towards both metals. One common expedient has been to add a lead-tin alloy containing at least 1% tin. Thus, at the interface between the copper and lead layers of the composite sheet, a ternary alloy comprising lead, tin and copper is present and provides the requisite bond. However, the presence of the tin (or other third constituent used) detracts from the purity of the overlying lead surface layer, and it is well-known that the presence of even minute proportions of impurities in the lead plating considerably lowers the impervious character of the plating, and the eifectiveness of the protection afforded by it to the underlying copper surface. The particles of foreign material, such as tin, present at the lead surface are points of incipient corrosion from which the attack spreads rapidly to the surrounding areas. The same can be said of the small surface defects that are inevitably present in the lead coating when applied by the conventional methods, especially dip-coating.

Objects of this invention are to provide a composite, copper-lead sheet material or laminate having greatly improved characteristics over comparable materials currently produced, especially in the purity and freedom from defects of the lead surface layer, as well as in the high strength of the bond at the copper-lead interface; to provide practical and economical electrochemical methods for the production of such sheet materials or laminates, including both simple copper-lead laminates and lead-copper-lead laminates; to provide such composite sheet material wherein the depth of the lead coating can be conveniently and controllably varied over a wide range, as from one tenth of a millimeter (or less), to ten or more millimeters. Other objects will appear.

The applicant has discovered the unexpected fact that copper-lead laminate material 'of extremely high characteristics, unattainable heretofore, can be obtained by electrodepositing lead onto a copper surface provided the copper surface itself is sufiiciently pure and free from 3,329,589 Patented July 4, 1967 any traces of oxidation (and phosphorus) and preferably has itself been obtained by electrodeposition. Thus in a preferred aspect of the invention, the process may comprise first electrodepositing a layer of copper and then using the deposited layer as a base for electrodepositing a layer of lead. Where a triple lead-copper-lead laminate is desired, the process may comprise electrodepositing a layer of lead, using this as a base for electrodepositing a layer of copper, and using this in turn to electrodeposit further a layer of lead, thereby providing a copper sheet lead-coated on both sides.

Such a process benefits from the extremely high uni-' formity characterising electrodeposition processes in general. Moreover, the absence of any extraneous bondformi-ng constituent, such as the tin commonly used heretofore, greatly heightens the purity of the product and correspondingly increases its corrosion-resistant properties.

Composite or laminate sheet materials, including both copper-lead and lead-copper-lead laminates, when produced by the electrolytic methods of the invention, and characterized by a high purity of the lead layer and the absence of any third constituent, as well as by an intimate continuous bonds at the interface or interfaces of the lead and copper layers, constitute new articles of manufacture included within the scope of the present invention.

Exemplary procedures and apparatus for carrying out the invention will now be described for purposes of illustration but not of limitation with reference to the accompanying drawings wherein:

FIG. 1 is a view in simplified vertical cross section of a first type of electrolytic cell usable in the process of the invention;

FIGS. 2 and 3 similarly illustrate two alternative types of electrolytic cells usable in further embodiments of the improved process.

The apparatus illustrated in FIG. 1 comprises a tank 1 which may be made of concrete internally lined with a suitable impervious plastic coating. The tank is filled with a body of electrolyte 2 the nature of which will be later specified. The tank further contains two anodes 3 and 4 having vertical upper portions extending along opposite sides of the tank and downwardly converging lower sections. Between the anodes is mounted a removable rotatable cathode structure 5 comprising a hollow cylinder or drum e.g. of cast iron secured on a shaft suitably journalled for rotation in the tank. Revolving-cathode electrolytic cells of this general kind are known so that the details thereof need not be described. The open V defined by the lower parts of the anodes 3 and 4 serves to reduce the variations in anode-cathode spacing to an acceptable value. A groove 6 is formed in the periphery of the revolving cathode drum 5 along a generatrix thereof and may have its surfaces coated wit-h a suitable insulating varnish to provide a gap in the metal sheet that will be electrodeposited around the drum 6. The drum is completely immersed in the electrolyte 2 and is supplied from a negative source at a terminal 7 connected with the shaft of the drum, while the anodes 3 and 4 are connected to the positive source at the terminal 8. A doctor blade 9, made of glass or the like, may be provided as shown (especially in the first, copper-depositing step of the process presently described), and is provided with means for imparting to it a rapid reciprocatory motion parallel to the axis of the cathode drum 5 to improve the uniformity of the deposited metal (copper) and avoid the formation of trees or the like. In the operation of the cell, as known per se, rotation of the cathode creates agitation in the electrolyte bath, promot ing smooth ion exchange reactions and enhancing the uniformity of the deposited layer.

It will be understood that the process being described includes two stages, the first of which electrodepositing a layer of copper around the periphery of the revolving cathode drum 6, and the second stage residing in electrodepositing a layer of lead over the copper sheet obtained in the first stage, while said sheet is positioned around the periphery of the same revolving cathode drum 6 transferred into an electrolytic cell similar to the one shown in FIG. 1, but arranged for the electrodeposition of lead.

In the first, copper-depositing stage of the process, the anodes 3 and 4 are made of copper which may be of a purity grade in the range e.g. from 98.5 to 99.0%. The electrolyte 2 may have the following composition: 60 to 80 grams per liter H 30 and 120160 g./liter copper sulfate CuSO-SH O. The bath temperature is in the range from 20 to 50 C. The direct current used .is in the range 3000-4000 amps. The cathode current density is about 4 amps/dm The voltage drop across the cell is about 2-3 volts. The electrical efficiency is about 96%. The cathode drum 5 is rotated at a speed of about 40 r.p.m. Electrolyte is circulated continuously over a flow circuit not shown, including suitable pumping and filtering means. A conventional amp-hour counter is preferably provided to measure the current flow through the cathode. This measurement may be indicated in units thickness deposited copper and can serve to control the deposited depth.

With the conditions indicated, copper deposits on the periphery of the cathode drum 5 at a rate of about 1 millimeter per 24 hours. The resulting copper sheet is of a purity grade of approximately from 99.95 to 99.97% and is completely free from oxygen and phosphor even in trace amounts. This condition is important for a successful performance of next stage of the process, now to be described.

The cathode drum 5 with the copper sheet obtained in the first stage is bodily removed from the electrolysis cell in which the copper sheet was formed, is rinsed free of electrolyte and is transferred to another cell, essentially similar to the one first described. In this cell however, the anodes 3 and 4 are made of substantially pure lead, and the electrolyte 2 comprises a suitable lead salt solution, e.g. an acidic lead fiuoroborate solution. One composition for the lead-plating electrolyte that has been successfully used, comprises from 70 to 120 g./liter of an aqueous solution containing 50% lead fluoroborate,

and from 0.10 to 0.30 g./l. gelatine. The bath temperature may be from to 40 C. The current characteristics may be the same as in the first stage. The rate of cathode rotation can also be the same. Lead is then found to deposit at a rate of about 0.15 millimeter per hour, and is chemically pure. The depth of deposited lead can be controlled in a manner similar to that used in the first stage, i.e. by measuring the amount of current that has flowed through the cathode. This provides an extremely convenient and accurate method of monitoring the depth of the deposited lead layer, which may be varied widely as from less than 0.1 to 10 mm. or more depending on requirement.

In the procedure just described, the product is a copper-lead laminated sheet. If it is desired instead to produce a lead-copper-lead sheet, then the process may be carried out in three stages rather than two; in the first stage, using an electrolytic cell with lead anodes and lead salt electrolyte, a layer of lead is deposited on the periphery of the removable cathode drum; this drum with the sheet of lead thereon is rinsed and transferred into another electrolysis cell having copper anodes and copper salt electrolyte; the cathode drum carrying the resulting copper-lead laminate can then be returned to the first cell, or placed in a similar cell, for depositing a further lead layer on the opposite side of the copper sheet. It will be evident that other sequences than the one described may be used if desired. However, the sequence just indicated is advantageous in that it permits the laminate to be retained on a single cathode drum throughout the process, thereby greatly facilitating handling operations. The surface of the cathode drum is preferably polished and slightly greased prior to the initial electroplating step to facilitate the subsequent removal of the final laminate sheet. The final sheet, after removal from the drum surface, may be passed through conventional straightening means and cut to size.

The copper-lead and lead-copper-lead laminates obtained in the manner described have a beautiful smooth, absolutely uniform aspect, with the cathode side being bright and the electrolyte side matte. No structural defects whatever can be detected in the lead surface. Microscopic examination of test-fractured sheets indicates a continuous, gradual transition between the lead and copper layers rather than a sharp interface there between, and the bond between the layers is extremely strong. As one very desirable consequence of this property, laminate sheets according to the invention can, in use, be subjected to various treatments, including soldering and welding operations for assembly, without any risk of delamination or tendency for the different-metal layers to separate. Soldering may be effected using pure lead, or lead-tin along containing not more than about 10% tin.

In the apparatus shown in FIG. 2, an electrolysis tank 10 made of concrete with an impervious plastic lining contains a body of electrolyte 11. Electrolyte circulating means 12 are provided including filter means 13, a circulating pump 14 and a valve 15. In this embodiment, a substantial rate of electrolyte circulation should be used in order to promote agitation in the bath and ion exchange reactions, in the absence of the revolving cathode of FIG. 1. A suitable range of flow rates with the apparatus described by way of example is approximately from 2 to 3 m. per hour and per in. of cathode surface.

Dipping into the electrolyte in the tank are lead anodes 16 (three shown) and intervening copper sheets 18 (two shown), that are to be lead-plated. The lead anodes are connected to positive terminal 17, and the copper cathodes are connected to negative terminal 19. It will be understood that in this embodiment the copper sheets 18 are assumed to have been produced separately by a method capable of yielding copper with the degree of purity required for practicing the lead-plating method of the invention, as by electrolysis. The current characteristics and electrolyte composition used may be substantially the same as indicated for the lead-plating stage in Example 1. The end product in this case is fiat copper sheeting lead plated on both sides.

The apparatus shown in FIG. 3 is used for lead-plating the outer surf-aces of copper tubes, for use in heat exchangers and other similar applications. An electrolysis tank 20 contains a body of electrolyte 21 which may be similar in composition to that indicated for the lead plating stage in Example 1. Supported on a suitable stand within the electrolyte is a set of spaced lead anodes 23, which are of the generally triangular prismatic form shown in order to minimize variations in anode-cathode spacing as described for the V-shaped anodes 3-4 in FIG. 1. Supported in spaced parallel relation between the adjacent lead anodes, for rotation about their axes, are a set of copper tubes 24 to be plated. The lead anodes are connected to positive terminal 26 and the copper cathodes are connected to negative terminal 25. Electrolyte circulating means include the conduit 22 with filter, pump and valve means therein as in FIG. 2. In view of the rotational mounting of the copper cathodes in this embodiment, the rate of flow of electrolyte through the system can be made substantially lower than in Example 2, a rate of about 1 m. per hour and per m? cathode surface being suitable.

In this procedure as in those earlier described, it is found that provided the copper tubes 24 to be plated are completely free from oxide and phosphorus impurities, the composite copper-lead tubes produced by electrodeposition have an extremely strong copper-lead bond. The high-purity -lead plating is perfectly smooth and uniform imparting a remarkably high degree of chemical protection to the underlying copper surface.

What I claim is:

1. A method of producing lead-plated copper sheet, comprising electrodepositing copper to a substantial thickness over the peripheral surface of a removable cathode having a polished, non-adherent peripheral surface and which is disposed in a first electrolysis cell having a copper anode and a copper-salt electrolyte, bodily transferring said removable cathode With the copper sheet on the periphery thereof into a second electrolysis cell having a lead anode and a lead-salt electrolyte, electrodepositing lead over the exposed periphery of said sheet in said second cell, and removing the resulting lead-plated copper sheet from said non-adherent peripheral surface of the cathode.

2. A method of producing copper sheet lead-plated on both sides thereof, comprising electrodepositing lead over a polished, non-adherent peripheral surface of a removable cathode in a first electrolysis cell having a lead anode and a lead-salt electrolyte, bodily transferring said cathode with the lead sheet thereon into another electrolysis cell having a copper anode and copper-salt electrolyte and electrodepositing copper to a substantial thickness over the exposed periphery of said lead sheet in said second cell, then bodily transferring said cathode with the copperplated lead sheet thereon into another electrolysis cell having a lead anode and a lead-salt electrolyte and electrodepositing lead over the exposed periphery of the copper plating of said sheet in said last mentioned cell, and removing the resulting copper sheet lead-plated on both sides from said non-adherent surface of the cathode.

References Cited OTHER REFERENCES Diggin, M, B.: Lead Plating, Metal Finishing, pages 418-422, July 1943.

Metals Handbook, page 1169, 1939.

Richards, E. T.: Electrodeposition of Lead, Metal Finishing, pages 59-64, February 1953.

JOHN H. MACK, Primary Examiner.

HOWARD S. WILLIAMS, Examiner.

G. KAPLAN, Assistant Examiner. 

1. A METHOD OF PRODUCING LEAD-PLATED COPPER SHEET, COMPRISING ELECTRODEPOSITING COPPER TO A SUBSTANTIAL THICKNESS OVER THE PERIPHERAL SURFACE OF A REMOVABLE CATHODE HAVING A POLISHED, NON-ADHERENT PERIPHERAL SURFACE AND WHICH IS DISPOSED IN A FIRST ELECTROLYSIS CELL HAVING A COPPER ANODE AND A COPPER SALT ELECTROLYTE, BODILY TRANSFERRING SAID REMOVABLE CATHODE WITH THE COPPER SHEET ON THE PERIPHERY THEREOF INTO A SECOND ELECTROLYSIS CELL HAVING A LEAD ANODE AND A LEAD-SALT ELECTROLYTE, ELECTRODEPOSITING LEAD OVER THE EXPOSED PERIPHERY OF SAID SHEET IN SAID SECOND CELL, AND REMOVING THE RESULTING LEAD-PLATED COPPER SHEET FROM SAID NON-ADHERENT PERIPHERAL SURFACE OF THE CATHODE.
 2. A METHOD OF PRODUCING COPPER SHEET LEAD-PLATED ON BOTH SIDES THEREOF, COMPRISING ELECTRODEPOSITING LEAD OVER A POLISHED, NON-ADHERENT PERIPHERAL SURFACE OF A REMOVABLE CATHODE IN A FIRST ELECTROLYSIS CELL HAVING A LEAD ANODE AND A LEAD-SALT ELECTROLYTE, BODILY TRANSFERRING SAID CATHODE WITH THE LEAD SHEET THEREON INTO ANOTHER ELECTROLYSIS CELL HAVING A COPPER ANODE AND COPPER-SALT ELECTROLYTE AND ELECTRODEPOSITING COPPER TO A SUBSTANTIAL THICKNESS OVER THE EXPOSED PERIPHERY OF SAID LEAD SHEET IN SAID SECOND CELL, THEN BODILY TRANSFERRING SAID CATHODE WITH THE COPPERPLATED LEAD SHEET THEREON INTO ANOTHER ELECTROLYSTS CELL HAVING A LEAD ANODE AND A LEAD-SALT ELECTROLYTE AND ELECTRODEPOSITING LEAD OVER THE EXPOSED PERIPHERY OF THE COPPER PLATING OF SAID SHEET IN SAID LAST MENTIONED CELL, AND REMOVING THE RESULTING COPPER SHEET LEAD-PLATED ON BOTH SIDES FROM SAID NON-ADHERENT SURFACE OF THE CATHODE. 